# pgr_makeConnected - Experimental¶

pgr_makeConnected — Set of edges that will connect the graph.

Warning

Possible server crash

• These functions might create a server crash

Warning

Experimental functions

• They are not officially of the current release.

• They likely will not be officially be part of the next release:

• The functions might not make use of ANY-INTEGER and ANY-NUMERICAL

• Name might change.

• Signature might change.

• Functionality might change.

• pgTap tests might be missing.

• Might need c/c++ coding.

• May lack documentation.

• Documentation if any might need to be rewritten.

• Documentation examples might need to be automatically generated.

• Might need a lot of feedback from the comunity.

• Might depend on a proposed function of pgRouting

• Might depend on a deprecated function of pgRouting

Availability

• Version 3.2.0

• New experimental function

## Description¶

Adds the minimum number of edges needed to make the input graph connected. The algorithm first identifies all of the connected components in the graph, then adds edges to connect those components together in a path. For example, if a graph contains three connected components A, B, and C, make_connected will add two edges. The two edges added might consist of one connecting a vertex in A with a vertex in B and one connecting a vertex in B with a vertex in C.

The main characteristics are:

• Works for undirected graphs.

• It will give a minimum list of all edges which are needed in the graph to make connect it.

• The algorithm does not considers traversal costs in the calculations.

• The algorithm does not considers geometric topology in the calculations.

• Running time: $$O(V + E)$$

## Signatures¶

pgr_makeConnected(Edges SQL)
RETURNS SET OF (seq, start_vid, end_vid)
OR EMPTY SET
Example:

Query done on Sample Data network gives the list of edges that are needed to connect the graph.

SELECT * FROM pgr_makeConnected(
'SELECT id, source, target, cost, reverse_cost FROM edges'
);
seq | start_vid | end_vid
-----+-----------+---------
1 |         5 |       2
2 |         4 |      13
(2 rows)



## Parameters¶

Parameter

Type

Description

Edges SQL

TEXT

Edges SQL as described below.

## Inner Queries¶

### Edges SQL¶

Column

Type

Default

Description

id

ANY-INTEGER

Identifier of the edge.

source

ANY-INTEGER

Identifier of the first end point vertex of the edge.

target

ANY-INTEGER

Identifier of the second end point vertex of the edge.

cost

ANY-NUMERICAL

Weight of the edge (source, target)

reverse_cost

ANY-NUMERICAL

-1

Weight of the edge (target, source)

• When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

Where:

ANY-INTEGER:

SMALLINT, INTEGER, BIGINT

ANY-NUMERICAL:

SMALLINT, INTEGER, BIGINT, REAL, FLOAT

## Result Columns¶

Returns set of (seq, start_vid, end_vid)

Column

Type

Description

seq

BIGINT

Sequential value starting from 1.

start_vid

BIGINT

Identifier of the first end point vertex of the edge.

end_vid

BIGINT

Identifier of the second end point vertex of the edge.